1. Field Of The Invention
The present invention pertains to the field of focused ion beam systems. More particularly, the present invention pertains to focused ion beam systems having integrated charge neutralization features and imaging features.
2. The Prior Art
There are numerous focused ion beam applications in which it is required to image and process targets made from materials which are electrically non-conducting. These applications include imaging and processes on passivated integrated circuits, photoresist-covered wafers and masks, benchmarks, and microanalyses of insulators or insulating inclusions in conducting or non-conducting substrates.
One particular application of focused ion beams is repair of photomasks. In mask repair, the surface of the mask is generally a very poor electrical conductor. Because of this, the ion beam causes a buildup of charge on the mask material. Thus, for repair of masks using focused ion beams, it is essential that charging of the mask surface is reduced or eliminated during both the imaging and repair processes. It is highly desirable that this charge neutralization is highly effective since target charging may increase the spot size, deflect the beam, and change the imaging behavior. The effect on the imaging behavior arises because the trajectories of secondary electrons and secondary ions (which have initial energies below 100 eV) are greatly affected by relatively small voltage differences on the mask surface.
Representative of prior art mask repair systems is the KLA/Micrion 808, Seiko SIR1000, and Ion Beam Systems MicroTrim. In all of these systems, the electron flood gun for charge neutralization is not integrated with the secondary electron or secondary ion collectors used for imaging the mask or other insulating surface. The disadvantage of each of these systems is that the operation of the flood gun and the imaging system is not optimized because these separate functions are not part of an integrated system. In general, these functions will actually interfere with each other unless they are designed together into one integrated system.
Additional prior art exists in the field of microanalytical instrumentation, such as systems manufactured by Vacuum Generators (e.g., MIQ 156), Riber, and Cameca (IMS-3f, IMS-4f). A particularly relevant example consists of a modification of the Cameca ion microprobe (ref. Secondary Ion Mass Spectrometry V, SIMS V, ISBN 0-387-16263-1, 1986, pp. 158-160, "The Emission Objective Lens Working as an Electron Mirror: Self-Regulating Potential at the Surface of an Insulating Sample", G. Slodzian, M. Chaintreau, R. Dennebouy). In this modification of the Cameca instrument, the flood beam is integrated with the signal collection optics, but in an entirely different manner from the present invention. This article illustrates one method for electron beam charge neutralization, however, the implementation described by Slodzian, et al., is inapplicable for use in a focused ion beam instrument because the primary ion beam is not integrated with the signal collection optics.